Artificial magnetic conductors (AMCs) are surface treatments that control the phase of reflection of an incident electromagnetic wave. AMCs are characterized by a resonant frequency, fres, at which where the phase of reflection is 0 degrees, and by their ±90 degrees bandwidth in which the reflected phase lies between −90 and +90 degrees. In general, AMCs may be constructed by applying a capacitive metallic grid on top of a dielectric substrate with a ground plane. The size of the grid and its period scales with the resonant frequency. The bandwidth scales with substrate thickness. Thus, as the target resonant frequency decreases, the grid period and the substrate thickness increases proportionately in order to maintain the same bandwidth.
To implement AMCs with sufficient and practical bandwidth at lower frequencies, such as in the VHF band (30-300 MHz) and in the lower end of the UHF band (300 MHz-3 GHz), the size of the structure must be scaled proportionally. By way of example, a 10 GHz AMC may be fabricated using relatively thin (e.g., 0.025-0.050″ thick) substrates of standard electronic circuit board material. By contrast, a VHF AMC requires substrate thickness between 0.500 to 1.00 inches, or even greater. Therefore, using standard electronic substrates is prohibitive for practical application because of availability, cost and weight. For example, a 1.00 inch thick AMC using Rogers Corp. 3010 substrate material will weigh more than 7.08 kg per square foot. Also, standard circuit board substrates have permittivity typically 2.0 or more. The higher the substrate permittivity, the lower the bandwidth of the AMC because the capacitance between the grid and the ground planes is proportional to the substrate permittivity.
Therefore, apparatus and methods to form AMCs capable of implementing relatively low-frequency (e.g., VHF and UHF band) communication may find utility.